Nigerians from a region devastated by oil spills on Monday called on the president to take action, more than a year after a United Nations report said the contamination may require the world's biggest cleanup.

“Every Ogoni person is a potential cancer patient,” Magnus Abbe, a senator and spokesperson for a delegation from the Ogoniland region of southern Nigeria, said during a visit to President Goodluck Jonathan with journalists present.

“Tragic and catastrophic as the situation is, the Ogoni people are concerned by a protracted and near absence of a strategic response by the federal government to the findings of the (UN) report.”

The president did not comment with journalists present, but later held a closed-door meeting with the delegation.

A landmark report from the UN's environmental agency in August 2011 said decades of oil pollution in Ogoniland may require the world's biggest clean-up.

The UN Environment Programme also called for the oil industry and the Nigerian government to contribute $1-billion to a clean-up fund.

It pointed out major health risks in the region of Africa's largest oil producer, including in one community where families were drinking water from wells contaminated with the carcinogen benzene at levels over 900 times above WHO guidelines.

Ogoniland was the native region of Ken Saro-Wiwa, the renowned environmental activist who was executed by a Nigerian military government in 1995 after what was widely considered a show trial, drawing global condemnation.

Shell, the biggest producer in Nigeria, was forced to leave Ogoniland in 1993 following community unrest sparked by poverty and allegations of environmental neglect, however pipelines still cross the area.

Despite the UN report, little action has been taken to clean up the region, which in part prompted the delegation's visit to Jonathan on Monday.